What semantic notions underlie 駁 (to rebut) with 馬 (horses) and/or 爻 (I Ching's hexagrams)?

Question

I'm trying to understand the etymology for definition 3 (to rebut) below in 駁 - Wiktionary. Yellowbridge:

Han character

駁 (radical 187, 馬+4, 14 strokes, cangjie input 尸火大大 (SFKK), four-corner 74340, composition ⿰馬爻)

豹 (OC *preːwɢs, “leopard”) is its exopassive derivative, literally meaning, "the spotted one".

Definitions

1. (of a horse's fur) variegated
2. mixed; heterogenous
3. to refute; to rebut
4. to transport by barge
5. barge
6. suddenly

I don't understand how 馬 or definition 1 (variegated horse's fur) relates to definition 3. So I looked up 爻 - Wiktionary, but I also don't understand how the I Ching's hexagram relates. I'm too addled to continue!

1. a figure composed of six stacked horizontal lines; a hexagram of the I Ching

Answer 1

Two notes:

• The original meaning of 「爻」 is criss-cross patterns, rather than I-Ching hexagrams;

• 「爻」 provides a phonetic hint to 「駁」.

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「駁」 (Baxter-Sagart OC: /*pˤrawk/, patterend/variegated horse fur) is composed of semantic 「馬」 (horse) and phonetic 「爻」 (/*N-kˤraw/). 「爻」 (criss-cross patterns) simultaneously provides a meaning hint.

The semantic extension is as follows:

1. Variegated horse fur

2. Impure/mixed colours and patterns (looking like a jumbled mess)

3. To distinguish, rectify (e.g. in the process of sorting out a jumbled mess, correcting what is chaotic/wrong)

4. To rebut (e.g. to refute falsehoods, denounce wrongdoing)

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References:

• 漢語多功能字庫
• 《漢語大詞典》